Subglacial Volcanism in North-Central British Columbia and Iceland

The subglacial genesis of five volcanoes in British Columbia has been confirmed by field and laboratory studies and by comparison with the stapar (table mountains) of Iceland. Two of the Canadian "tuyas" are flat-topped piles of hyaloclastite overlain by basalt flows. These mountains are almost identical in form to their Icelandic counterparts. Three other tuyas are large conical piles of unconsolidated lapilli, two of which overlie vitric tuff and pillow basalt layers, and may be analogous to relatively rare Icelandic subglacial scoria cones. All five volcanoes can be accounted for by eruption into englacial meltwater lakes. The differences in gross morphology and physical composition can be accounted for by minor variations in the relative importance of magmatic versus phreatomagmatic eruption.